Between 1990 and 1994, the national incidence of reported infections ranged from 3 to 5.3 per 100,000 inhabitants.

Most cases are sporadic and are caused by E. coli O157 : H7.

Recent investigations have identified that, in addition to exposure to undercooked ground beef, contact with cattle, consumption of well water, and exposure to rural environments are important risk factors for VTEC infection.

Also, results of case-control studies and detection of asymptomatic fecal carriage of E. coli O157 : H7 and other VTEC in farm family members and abattoir workers have led to an increasing emphasis on person-to-person spread in the epidemiology of VTEC infection.

Controlling E. coli O157 : H7 and other VTEC at the farm level may therefore have a broader impact than simply reducing the risk of foodborne VTEC infection.

Longitudinal studies on dairy farms have demonstrated that E. coli O157 : H7 carriage by cattle at the farm and animal level is often transient, and that cattle, rather than the farm environment, are the major reservoir for this organism on dairy farms.

Small herds that are controlled by traditional management practices have the highest risk for VTEC infection.

Further studies are likely to result in development of effective strategies to control VTEC at the farm level.